This invention relates to the hermetic packaging of microcircuits, and, more particularly, to an approach for improving the sealing of the package.
Integrated circuits, also termed microchips, are electronic devices that are extremely miniaturized, so that hundreds or even thousands of individual circuits and active elements fit into a space that may be only 1/2 inch on a side. The microchips themselves are small and fragile. They must therefore be packaged and protected in a manner that permits external electrical connections to be made, and permits the integrated circuits to be handled in a normal manner during the assembly and repair of electronic devices that may utilize the microcircuits.
One approach to packaging the microchips is to mount them on a ceramic base having electrical connector pins extending through the base and sealed to the base to be gas tight. Electrical connection pads on the microchip are connected to the pins with fine wires and conducting paths called traces. A ceramic cover or lid having a recess therein to accommodate the microchip is placed over the upper surface of the base, with a sealing surface of the lid contacting the upper surface of the base.
The lid is sealed to the base with a layer of a flowable material, preferably a glass, that is placed between the upper surface of the base and the sealing surface of the lid. The package is heated to a temperature at which the glass flows, effecting the seal. The final package is desirably completely sealed against the intrusion of gases, moisture, and potentially damaging chemicals from the environment into the interior of the package, ensuring the operation of the microchip even in adverse circumstances.
While this sealing approach is desirably accomplished, it has been observed by many companies in the industry that there are faults in the seal between the base and the lid in a fraction of the packages. These faults are sometimes apparent to the eye, and in other cases are discovered only by X-raying the package. The faults may extend through the entire width of the sealing surface from the interior to the exterior, so that in fact no complete seal is achieved. In other cases, the fault extends through a portion of the width of the sealing surface, making its detection more difficult. Even in these cases, the fault can permit the flow of gas or liquid into the interior of the package over a period of exposure, leading to accelerated failure of the microchip.
There exists a need for an improved sealing approach for hermetic microchip packages to achieve an unfaulted seal that provides both initial and extended-term hermetic sealing of the microchip in the package. The sealing approach should be highly reliable, and should not be excessively expensive to implement. The present invention fulfills this need, and further provides related advantages.